The present invention relates to a conveyor belt and more particularly to a conveyor belt having a light weight, a high tensile force, and an excellent durability.
In general, a conveyor belt comprises an endless belt body of a rubber, a thermoplastic resin, a thermosetting resin or the like and a reinforcing layer embedded in the belt body along the longitudinal direction of the belt body.
A canvas conveyor belt wherein the reinforcing layer is formed of a woven fabric of an organic fiber exemplified by a nylon fiber or a polyester fiber and a steel cord conveyor belt wherein the reinforcing layer is formed of a steel cord are known in the art. In general, the canvas conveyor belt generally has an advantage that it is lighter than the steel cord conveyor belt. Since, however, the tenacity of the canvas conveyor belt is lower than that of the steel cord conveyor belt, the canvas conveyor belt is unsuitable as a conveyor belt which is required to have a high tenacity of not less than 500 kgf/cm.
On the other hand, the steel cord conveyor belt is constructed so that a plurality of steel wires are twisted into a steel cord having a large diameter of about 2 to 15 mm and high tenacity and a plurality of the steel cords are embedded substantially parallel to each other or one another in a belt body along the longitudinal direction of the belt body without using any weft unlike a woven fabric. The use of the steel cord having high tenacity enables finger splicing at an endless joint with a high joint efficiency (joint strength), advantageously offering a conveyor belt which can withstand high tension.
Since, however, in the steel cord conveyor belt, the reinforcing layer is formed of a steel cord, a problem of large weight occurs. In addition, the use of the steel cord poses a problem that the conveyor is rusted, for example, by penetration of water during use in humid environment or due to cracking of the rubber, which is likely to cause adhesion failure or breaking of the cord. Further, the disposal of used conveyor belts is very troublesome.
Worsening of environmental problems and economic environment in recent years have given rise to a strong demand for a conveyor belt having smaller weight, higher tenacity, and longer service life.
In order to solve the above problems involved in the steel cord conveyor belt and the above demand to the conveyor belt, a conveyor belt has been developed wherein an aramid fiber (an aromatic polyamide fiber) having high tenacity among the organic fibers is used in a woven fabric form as the reinforcing layer.
In the conveyor belt using a woven fabric of an aramid fiber in the reinforcing layer, even when a finger splice structure offering the highest endless efficiency is applied to the endless joint, there is a limitation on the joint strength due to the nature of the woven fabric structure of the reinforcing layer, limiting the tenacity to up to about 2000 kgf/cm from the practical viewpoint.
Even though a method for forming an endless structure with a very high endless efficiency could be developed, the woven fabric structure of the aramid fiber cannot satisfactorily utilize high strength inherent in the aramid fiber, and it is substantially impossible to prepare a woven fabric having a tenacity exceeding 2000 kgf/cm and high durability. Further, the woven fabric structure has a drawback that the creation of a notch, such as cracking, at both ends in the widthwise direction of the conveyor belt is likely to cause stress concentration, resulting in breaking of the woven fabric at the crack.
For this reason, the development of a novel conveyor belt, which is light weight and usable in applications where a tenacity exceeding 2000 kgf/cm is required, has been desired in the art.